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    <title>Document</title>
    <style>
        .outer_container{
            font-size:20px;
            font-weight: 500;
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    <script>
        window.onload = function(){
            //------1
            // var a = {n:1}
            // var b = a
            // console.log(a,"前")
            // console.log(b,"前")
            // console.log(a == b)
            // a.x = a = {n:2}
            // console.log(a,"后")
            // console.log(b,"后")
            // console.log(a.x)//undefined 
            // console.log(b.x)//{n:2}

            //------2
            // var arr = [0, 1, 2]
            // arr[10] = 10
            // console.log(arr.filter(function (x) {
            //     return x === undefined
            // }))

            //------3
            // var name = 'World'
            // ;(function () {
            // if (typeof name === 'undefined') {
            //     var name = "Jack"
            //     console.info('Goodbye ' + name)
            // } else {
            //     console.info('Hello ' + name)
            // }
            // })()

            //------4
                                  
        }

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        h5客户端
    </div>
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